Sulfur is a promising cathode active material with a high theoretical specific capacity, low cost, and environmental benignity. Nevertheless, it is difficult to develop a practical secondary battery without problems such as the low electrical conductivity of sulfur, dissolution of polysulfides in electrolyte, and volume expansion of sulfur during discharge. These problems result in poor cycle life, low specific capacity, and low energy efficiency.
Carbon materials, such as active carbon, carbon nanotubes, mesoporous carbon, or graphene are combined with the sulfur to help remedy some of the problems. However, there has been difficulty uniformly combining sulfur and the carbon materials which limits the cycle life of the secondary battery.
What is needed, therefore, is to provide a method for making a sulfur-graphene composite material which can improve the cycle life of the secondary battery having the sulfur-graphene composite material used as a cathode active material.